The subject invention relates to a device in fluid pressure generators of the kind comprising an annular casing which is peripherally mounted and driven in a through-flow channel and wherein the inner face of said casing forms part of the wall of the fluid through-flow channel, said casing being equipped with a number of propeller blades which project radially inwards into the through-flow channel.
In propelling mechanisms for propulsion, steering and positioning of e.g. ships and oil rigs, the power losses are considerable. To compensate for such power losses, which have many causes, it is necessary to exaggerate the dimensions of the propeller and its prime mover with resulting the high costs.
By using a nozzle the degree of efficiency of propelling mechanisms may, as a rule, be increased. This is due to the concentration of the propelled flow by the nozzle. However, the gains are largely countered by the disadvantage caused by the necessity to provide the nozzle with shaft supports and with bearings supporting the propeller and these components together with the propeller hub result in considerable losses due to friction when the water flows through the nozzle.
Other considerable power losses are caused by the recirculating or turbulent fluid flow from the pressure faces of the propeller blades around the apices or the ends thereof towards the suction side of the blade. Because of the necessity to arrange for some clearance between the propeller blade apices and the inner wall of the nozzle this kind of power losses remains in propeller mechanisms equipped with nozzles.
Annular propelling mechanisms which are peripherally mounted and driven are known from e.g. SE-PS 342 011. These mechanisms are intended for propulsion and channel-steering systems in ships. Because the propeller, as mentioned above, is mounted at the periphery of the through-flow channel the losses therein due to friction are small. In addition, the need for clearance at the propeller blade apices is eliminated and losses connected with this arrangement therefore are almost entirely avoided. However, this prior-art publication does not provide a practical solution to the problem of how to use the mechanism for instance in channel steering systems. Since the blades are fixed in such annular propelling mechanisms the rotational direction must be reversible, which obviously means that the propeller must be stopped before it can rotate in the opposite direction. This appears from FIG. 13 of that publication and the text pertaining thereto. For this reason this prior-art propelling mechanism cannot be used with the required degree of reliability to propel e.g. passenger ferries to moor them alongside quays or in steering systems to position oil rigs and the like for drilling operations, for depositing pipelines or for driving operations in deep sea areas. Nor does SE-PS 341 011 suggest any satisfactory solutions to the problem of peripheral mounting of the annular propelling mechanism. Water-lubricated rubber bearings are suggested for the purpose. During normal operating temperatures. e.g. between appr. -4.degree. C. and about +15.degree. C. and for normal yearly operational periods of up to 8000 hours this kind of mounting of the annular propelling mechanism is not, however, particularly reliable.